The effector functions mediated by the Fc region of an antibody allow for the destruction of foreign entities, such as the killing of pathogens and the clearance and degradation of antigens. Antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cell-mediated phagocytosis (ADCP) are initiated by binding of the Fc region to Fc receptor (FcR)-bearing cells, whereas complement-dependent cytotoxicity (CDC) is initiated by binding of the Fc region to C1q, which initiates the classical route of complement activation.
Fc-mediated effector functions, such as ADCC and complement activation, have been suggested to contribute to the therapeutic efficacy of monoclonal antibodies used for the treatment of cancer (Weiner et al. Cell 2012, 148:1081-1084).
Previous efforts have been made to reduce unwanted effects caused by binding to the Fc region, e.g. cytokine storm and associated toxic effects or platelet aggregation, by providing antibody fragments or antibodies with mutated amino acid sequences. For example, antibody fragments, such as Fab, F(ab′)2, or scFv molecules, intrinsically lack Fc-effector functions, but have a short in vivo half-life and may require additional modifications to extend the half-life. Tao and Morrison (1989) describes studies of aglycosylated chimeric mouse-human IgG. Bolt et al. (1993) describes generation of a humanized, non-mitogenic CD3 monoclonal antibody which retains in vitro immunosuppressive properties.
Canfield and Morrison (2003) describes the binding affinity of human IgG for its high affinity Fc receptor is determined by multiple amino acids in the CH2 domain and is modulated by the hinge region.
Hezarah et al. (2001) describes effector function activities of a panel of mutants of a broadly neutralizing antibody against human immunodeficiency virus type 1.
Armour et al. (2003) describes differential binding to human FcgammaRIIa and FcgammaRIIb receptors by human IgG wildtype and mutant antibodies.
Idusogie et al. (2000) describes mapping of the C1q binding site on rituxan, a chimeric antibody with a human IgG1 Fc.
Shields et al (2001) describes high resolution mapping of the binding site on human IgG1 for FcγRI, FcγRII, RcγRIII, and FcRn and design of IgG1 variants with improved binding to the FcγR.
Oganesyan et al. (2008) describes structural characterization of a human Fc fragment engineered for lack of effector functions.
Duncan et al. (2008) describes localization of the binding site for the human high-affinity Fc receptor on IgG.
Parren et al, (1992) describes the interaction of IgG subclasses with the low affinity Fc gamma RIIa (CD32) on human monocytes, neutrophils, and platelets.
Newman et al (2001) describes modification of the Fc region of a primatized IgG antibody to human CD4 retains its ability to modulate CD4 receptors but does not deplete CD4(+) T cells in chimpanzees.
Alternatively, the hinge region of the antibody has been reported to be of importance with respect of interactions with FcγRs and complement. Dall'Acqua et al (2006) describes modulation of the effector functions of a human IgG1 through engineering of its hinge region. However, none of the previously engineered Fc regions are completely devoid of Fc-mediated functions. Furthermore, the impact of these specific mutations on immunogenicity and in vivo half-life is often unknown.
As described above, there is a need of proteins incapable of inducing a range of specific effector functions and at the same time have conserved pharmacokinetic properties. The present invention provides such proteins.